Biochemical oxygen demand in rivers (source: EEA)

Biochemical oxygen demand (BOD) is used to measure water quality. It refers to the amount of oxygen required by aerobic microorganisms to decompose organic substances in a water sample over a period of five days in the dark at 20°C (BOD5), measured as milligrams per litre (mg O2/L) and weighted by the number of measuring stations. High values of BOD5 are usually a sign of organic pollution, which affects the water quality. The cleanest rivers have BOD5 values of less than 1 mg O2/L, moderately and heavily polluted rivers show values ranging from 2 to 8 mg O2/L. Only complete series after inter/extrapolation are presented. For details on the total of measuring stations and their distribution over the countries, please consult the metadata file.